Matrix-isolation infrared and computer simulation spectra of M(CH3)nCl4−n (M = Si,Ge and Sn) type compounds in the M-C and M-Cl stretching regions

The IR spectra of the M(CH₃)_nCl_4?n (M = Si, Ge and Sn; n = 4,3,2 and 1) type compounds have been measured in argon and nitrogen matrices at ~ 15 K. The isotope structures have been observed for most of the M-C and M-Cl stretching bands, and assigned by using the computer simulation technique. Relative displacements of individual atoms have been calculated from the observed isotope shifts.     

Torsional transitions and barrier to internal rotation of 1,2-butadiene

The far i.r. spectrum of 1,2-butadiene (methyl allene) has been recorded in the gas phase from 370 to 40 cm⁻¹ with a resolution of 0.1 cm⁻¹. The methyl torsional fundamental has been observed for the first time at 154.3 cm⁻¹, along with some accompanying torsional hot bands. From these data the barrier to internal rotation has been calculated to be 556 cm⁻¹ (1.59 kcal/mol). Detailed K-structure has also been observed for both A—A and E—E torsional transitions and considered in the analysis. SCF calculations have been made for the structure and energies of conformers, so that both kinetic and potential constants for internal rotation have been obtained. The a′ skeletal fundamental is observed at 201.8 cm⁻¹ as a much stronger band than the torsional mode, and the a″ skeletal fundamental gives rise to an even stronger band at 319.8 cm⁻¹.     

The microwave spectrum,structure and centrifugal distortion constants of 2-chloroacrylonitrile

The microwave spectrum of 2-chloroacrylonitrile has been studied in the 26.5–40 GHz region. A total of 99 a- and b-type rotational transitions have been measured and assigned for CH₂ =C³⁵Cl(CN),yielding values for the rotational constants (in MHz): A = 6973.27, B = 3148.16, C = 2165.95. For CH₂=C³⁷Cl(CN) a total of 53 transitions have been measured and assigned and the rotational constants obtained are (in MHz): A = 6909.35, B = 3081.17, C = 2127.98. The distortion effects have also been studied and the quartic distortion constants have been evaluated. From the observed hyperfine structure, the chlorine nuclear quadrupole coupling constants have been obtained. The structure of vinyl cyanide and vinyl chloride can be transferred to account remarkably well for the observed rotational constants.     

Synthesis of p-coumaroylquinic acids and analysis of their interconversion

The synthesis of four isomers of p-coumaroylquinic acids was performed by esterification of p-acetylcoumaroylchloride with a suitably protected (?)-quinic acid. All isomers have been characterized by means of NMR spectroscopy and circular dichroism. Acyl migration was observed in the synthesis of 3-O-p-coumaroylquinic acid and 4-O-p-coumaroylquinic acid. Calculations on the most stable conformations of all isomers have also been performed to explain the acyl migration observed during the synthesis procedure.     

The Raman active internal vibrational modes of potassium nitrate

The Raman active internal vibrational modes of single crystal orthorhombic potassium nitrate have been studied in various polarizations. The full multiplet structure predicted by factor group analysis for the v₂ and v₃ regions has been observed for the first time. The expected site group splitting of the v₄ mode was not observed and can be assumed to be less than 0.5 cm^?1.     

Infra-red and electronic absorption spectra of 2-bromopyrimidine

The electronic absorption spectrum of 2-bromopyrimidine in the u.v. region has been recorded in vapour phase and in solution phase in different solvents. Only one system has been observed in vapour phase and it has been identified as π* ← n transition. In solution phase two systems have been identified. The system on the longer wavelength side has been identified as corresponding to the one observed in vapour phase while the other one has been assigned to a π* ← π transition. The infrared spectrum of this molecule has also been recorded and analysed. Help of these i.r. data has been taken to analyse the u.v. spectrum of 2-bromopyrimidine, considering the molecule as belonging to C_2υ point group.     

Free radicals derived from 1,4-diaza-1,3-butadiene: II. Adducts with metal carbonyls and reactions with derivatives of group VB elements

The paramagnetic adducts formed when photochemically generated Mn(CO)₅ or Re(CO)₅ radicals are trapped by N,Nt?-di-t-butyl-1,4-diaza-1,3-butadiene (t-Bu-DAB) have been characterized by ESR spectroscopy. Adducts containing phosphorus have also been observed but attempts to produce adducts containing As, Sb or Bi have been unsuccessful. In a number of systems an identical ESR spectrum was observed. This has been shown to arise from the N,N′-di-t-butylpyrazinium cation.     

Neutron inelastic scattering spectra and phase transition of 1,2-dichloroethane crystal

Neutron inelastic scattering spectra of 1,2-dichloroethane crystal have been measured at three temperatures above and below 177°K where the crystal undergoes a broad phase transition. Two and three peaks have been observed in the high and low temperature phases, respectively. The frequency distribution g(v) has been calculated in the first Brillouin zone for the low temperature phase and is compared with the observed spectra. The results show that the phase transition at 177°K is associated with rotational motion of the molecule around the axis passing through two chlorine atoms.     

Vibrational spectra of the trans-trans and trans-cis conformers of dimethyl fumarate

Infrared and Raman spectra of dimethyl fumarate (DMFU) have been recorded in the temperature range 12–390 K. The solid state spectra are consistent with the trans-trans conformation. However, in the liquid phase (melt or solution in CCl₄) and in the vapour phase, additional infrared and Raman bands were observed due to the presence of the trans-cis conformer. For the trans-trans conformer the observed spectra have been assigned on the basis of a C_2h molecular symmetry. A normal coordinate analysis of trans-trans DMFU has been carried out using a modified Urey- Bradley force field to assist in the assignment. Observed frequencies for the trans-cis conformer have been assigned on the basis of a structure of C_s symmetry.     

Chirped-pulse Fourier transform microwave spectroscopy of perfluoroiodoethane

The pure rotational spectrum of perfluoroiodoethane between 8.0 and 11.9 GHz has been measured on a search accelerated, correct intensity Fourier transform microwave (SACI-FTMW) spectrometer. The spectra is dense with 247 measured transitions in the given region. Only the anti conformer was observed for which rotational constants are reported. Nuclear electric quadrupole coupling constants due to the iodine-127 were determined and are reported. Also, two dipole forbidden/quadrupole allowed ΔJ=2 transitions were observed in the spectra. The observation of these transitions has been rationalized on the basis of near degeneracies between energy levels connected by χ_ab.     

Optically detected zero-field triplet state magnetic resonance in photosynthetic bacteria

Triplet state transitions of the photosynthetic bacteria Rhodospirillum Rubrum, Rhodopseudomonas Spheroides and Chromatium Vinosum in chemically reduced preparations have been observed by zero-field optical detection of magnetic resonance at 2 K. For each bacterial preparation two sharp, structureless, zero-field EPR transitions were observed as microwave-induced decreases in the fluorescence intensity of the frozen cellular preparations. The depopulating rate constants for the spin sublevels of the triplet states observed in R Rubrum and R Spheroides were also measured. The similarities of the triplet state frequencies, spectral features and intersystem crossing rates suggest a common structure for the reaction centers in the photosynthetic bacteria.     

Quasi-linear fluorescence and phosphorescence of some aromatic and heterocyclic compounds in tetrahydrofuran at 77 K

The fluorescence and phosphorescence emission spectra of 31 polynuclear aromatic hydrocarbons and a number of heterocyclic compounds have been studied in tetrahydrofuran and in n-paraffin solvents at 77 K. A comparison of the characteristics of the quasi-linear luminescence emission observed in these solvents has been made. The effect of the presence of peroxide impurities in the tetrahydrofuran solvent on the emission spectrum observed for coronene has been investigated.     

EXFAS electron spectroscopy as a new tool of local characterisation of copper in Cu-Beta zeolite

EXFAS spectroscopy has been applied for the first time to the study of the local characterisation of reduced copper in zeolites. The oscillating features observed beyond the Cu M_2,3VV Auger transition have been isolated and analysed following the standard EXAFS procedure.     

Vibrational spectra and structure of dimethyl oxalate and dimethyl oxalate-d6

The vibrational spectra of dimethyl oxalate-d₆, have been examined in connection with a re-examination of the spectra and structure of dimethyl oxalate. The vibrational spectra of the compound had previously been interpreted as being consistent with a transC_2h structure in the solid phase and a non-planar C₂, form in the liquid and gas phases. This behaviour is not consistent with that observed in similar compounds and a re-evaluation of the facts suggests that the major spectral changes which are observed may be caused by destroying an intermolecular association in going from the solid to the liquid phase, which allows the methyl groups to assume positions out of the plane. Some modifications and additions have been made in the vibrational assignment and assignments are presented for the deuterated compound.     

Anomalous fluorescence spectra of 1-isopropylidene-1H-cyclopent[a]azulene and 3-isopropylidene-3H-cyclopent[a]azulene

The electronic and fluorescence spectra of 1-isopropylidene-1H-cyclopent[a]azulene and 3-isopropylidene-3H-cyclopent[a]azulene, which are iso-π-electron systems of benz[a]azulene, have been measured. Anomalous fluorescence spectra have been observed for both compounds. It has been concluded that these compounds emit fluorescence from the second excited singlet state.     

13C-NMR study of cresyl benzoates

The proton-decoupled ¹³C FT—NMR spectra of para-, meta- and ortho-cresyl benzoates have been recorded and the observed signals have been assigned following the substituent additivity rule. The important features of diagnostic value of these spectra are discussed.     

A measurement of vibrational excitation in NO produced in the photodissociatton of NOCl and NOBr at 193nm

Infrared emission has been observed from the vibrational state v_n (n from 1 to ? 16) of the nascent NO(X²Π) photo-fragment produced in the photodissociation of NOCl and NOBr at 193 nm. The photodissociation was observed to be a single-photon process. Models and mechanisms of photodissociation are discussed in view of experimental observations.     

Kinetic study of the acid hydrolysis of sucrose and lactose and kinetic determination of sucrose using a periodate-selective electrode

A novel procedure for the kinetic study of the acid hydrolysis of sucrose and lactose has been developed. The parameter observed is the rate of the reaction of periodate with quenched aliquots of the solution in which hydrolysis takes place. This rate measured with a periodate-selective electrode, and is expressed in terms of rate of increase in potential (gDE/Δt). Based on the observed differences in the hydrolysis rate, a kinetic method has been developed for the determination of sucrose in the presence of other carbohydrates in the concentration range 0.01–0.10 M with an average error of 1.4%. The method has been applied to the determination of sucrose in milk products and soft drinks.     

Evaluation of dipolar shifts and paramagnetic anisotropy in penta coordinated cobalt(II) complexes

The isotropic proton shifts for the pyridine N-oxide and γ-picoline N-oxide protons have been observed in the penta coordinated adducts of these bases with bis[di(p-tolyl)dithiophosphinato] cobalt(II). The contribution to the observed shifts due to dipolar interaction has been calculated. From the dipolar shifts, it was ascertained that the pyridine N-oxide complexes have a bent structure in solution with a Co-O-N angle of 125°. An estimate of the paramagnetic anisotropy of the cobalt complex yields K_?-K_⊥ = 4244 × 10^?6 cm³/mole.     

Analysis of the 5p6p configuration of Xe V

The spectrum of four times ionized Xenon (XeV), has been observed in the 500–6800 Å range and 84 new lines have been identified as transitions between levels of 5s5p ³, 5s ²5p5d, 5s ²5p6s, 5s ²5p ², and 5s ²5p6p configurations. Nine new levels belonging to the configuration 5p6p have been determined. The results of this analysis are supported by Hartree-Fock calculations. The configurations are interpreted by fitting the theoretical energy parameters to the observed levels using least-squares techniques.